Coffee fans rejoice. This particular incarnation as a coffee ice cream sundae with a whiskey-spiked caramel sauce is so insanely good, we suspect you’ll be indulging in this far more often than the drink itself!
2Preheat oven to 325°F with rack in middle. Line a rimmed sheet pan with a nonstick baking liner, or line it with foil and lightly oil foil.
3Whisk egg white with sugar, coffee powder, and salt in a bowl until blended. Stir in walnuts until coated. Spread mixture into a 10- by 8-inch rectangle in pan.
4Bake until crisp is dry to the touch, 20 to 25 minutes. Transfer pan to a rack to cool completely.
5Loosen crisp with a metal spatula and break into small pieces.
6For Sauce and Sundaes:
7Bring sugar and water to a boil in a 2-quart heavy saucepan over medium-high heat, stirring until sugar is dissolved. Boil without stirring, but washing down any sugar crystals with a brush dipped in cold water, until syrup begins to turn golden, about 5 minutes.
Continue to boil, swirling pan occasionally, until syrup is a deep golden caramel.
8Remove pan from heat and carefully add whiskey, cream, and salt (mixture will bubble up and steam and caramel will harden).
9Return pan to heat and simmer, stirring, until caramel is dissolved and sauce is smooth. Cool to warm.
10Serve sauce over scoops of coffee ice cream then sprinkle with walnut crisp.
Crisp can be made 4 days ahead and kept in an airtight container at room temperature. (Watch out, though; it’s so delicious, you will be hard-pressed to resist devouring all of it before your guests arrive!)
Sauce can be made 4 days ahead and chilled, covered. Rewarm to serve. Any leftover sauce will keep, chilled, at least 1 week